Heretofore, butyl rubber, i.e., copolymers of isobutylene and small amounts of isoprene as a comonomer, and/or halobutyl rubbers, i.e., a halogenated derivative of a butyl rubber, have been used as an elastomer for forming blend compositions with thermoplastic compounds and other elastomer compounds for use in tire production and the like. The butyl and/or halobutyl rubbers impart a number of desirable physical properties to such blends, such as low air permeability, relatively low glass transition temperature (Tg), broad damping peaks, environmental aging resistance, etc. that are significant in the production of tires of superior performance properties. However, various difficulties are encountered with the use of the butyl and/or halobutyl rubbers for this purpose, chief among which is their high incompatibility with most other polymers, including even unsaturated elastomeric compounds to which they have weak adhesion. Hence, that aspect of a butyl rubber that provides properties which make it desirable as a component in blends for tire production, namely the chemical "inertness" that results from the unreactiveness of the hydrocarbon backbone of the butyl rubber polymer, also results in its low reactivity and incompatibility with most other materials and this has limited its use in many areas.
Recently, in U.S. Pat. No. 5,162,445 a unique copolymer of isobutylene has been disclosed together with a procedure for introducing non-backbone functionalities into the copolymer, which well suits it to use as a blend component having all the property advantages of a butyl and or halobutyl rubber, but which overcomes the incompatibility disadvantage of a butyl and/or halobutyl rubber. In its broadest description, the new copolymer is a direct reaction product of an isoolefin having from 4 to 7 carbon atoms with a para-alkylstyrene (PAS); isobutylene (IB) and para-methylstyrene being the preferred monomers; wherein the copolymer has a substantially homogeneous compositional distribution. Derivatives of this IB-PAS copolymer having functionalities that render it compatible and/or cross-linkable with other polymer materials, both thermoplastic and elastomeric polymers, are produced through a halogenated intermediate that is produced by a free radical initiated halogenation of the IB-PAS copolymer.
In U.S. Pat. No. 5,162,445 a preferred copolymer is that of isobutylene and para-methylstyrene and this copolymer is brominated to provide a copolymer having a portion of its para-methylstyrene content brominated at the para-methyl group. The brominated copolymer is essentially a high molecular weight, narrow molecular weight distribution polymer of isobutylene-para-methylstyrene-para-bromomethylstyrene. The benzylic bromine atoms are highly reactive under mild conditions in the presence of a nucleophilic reagent. It was found that a wide variety of functional groups could be introduced at the site of the brominated para-methyl carbon atoms of the pendent phenyl groups to displace at least a portion of the bromine atoms without disruption of the backbone structure or altering the molecular weight and/or molecular weight distribution characteristics of the backbone of the copolymer.
Heretofore, styrenic polymers have reportedly been metalated with lithium by reaction with an alkyl lithium compound activated with N,N,N',N'-tetramethylethylenediamine (TMEDA), and the metalated derivative then converted by reaction with an electrophilic reagent to a variety of functionalized derivatives. Harris et al. U.S. Pat. No. 4,145,490 and Macromolecules, 19, 2903-08 (1986) describe the metalation of copolymers of isobutylene with styrene and/or a metalated styrene with lithium as a means of introducing functionality into the copolymer to prepare it for polymerization with pivalolactone. The procedure described by Harris et al. apparently results in introducing functionality into both the primary and tertiary benzylic carbon atoms of a methylated styrene comonomer unit, as well as the aromatic ring carbon atoms thereof. Huge excess of the reagent (alkyl-Li/TMEDA) is required, yet only partial metalation is achieved, and long reaction time are some of the disadvantages associated with the Harris et al. procedure. Hence, it appears that the possible advantage of following the Harris et al. procedure as a means for introducing functionality into the new IB-PAS copolymers disclosed by U.S. Pat. No. 5,162,445 would be achieved at the significant disadvantage of disrupting the hydrocarbon nature of the backbone chain of this copolymer by also introducing lithium at the tertiary benzylic carbon atoms of the copolymer backbone.
Reports have also appeared concerning the combination of an alkyl lithium compound with an alkoxide of a heavier alkali metal to form a reagent, which has been referred to as a "superbase," which is very reactive for performing metalation reactions in organic synthesis and polymer chemistry. The application of a superbase reagent formed from an alkyl lithium and a potassium alkoxide to the metalation of aromatic hydrocarbons like benzene, toluene, ethylbenzene, and cumene to form a metalated species in which the counterion is the heavier alkali metal rather than lithium have been described in articles like J. Organometalic Chemistry, 28, 153-158 (1971); J. Organometalic Chemistry, 326, 1-7 (1987); Tetrahedron Letters, 32, 1483-86 (1991); Macromolecules, 29, 6081 (1976).
Even with respect to such simple aromatic molecules, a variety of intermediate metalated products, as deduced from the product resulting from the reaction of the metalated intermediate with methyl iodide, have been reported. In addition to the products whose structures were not determined, the other products of the alkyl Li/K alkoxide superbase metalation reaction comprise structures wherein both an alkyl side chain carbon atom and/or an aromatic ring carbon atom are metalated.
Lochmann et al. in Ploym. Mat. Sci. Eng., 69, 426-7 1993) and Polymer Preprints, 34(2), 588-9 (1993) have described the metalation of homopolystyrene and a dendritic polyether with an alkyl Li/potassium tert-pentoxide superbase reagent as a means for introducing functionalities whereby the functionalized polymer materials may then be converted to graft copolymers or multifunctionalized dendrimers of significantly altered properties. It is again reported that main chain metalation--i.e., metalation of the tertiary benzylic carbon atom of the polymer backbone chain--occurs to an even greater extent with an alkyl lithium/potassium tert-pentoxide superbase reagent than that which occurs with an alkyl lithium/TMEDA reagent like that used previously by Harris et al. The metalation of such backbone carbon atoms would disrupt the hydrocarbon nature of the polymer backbone of the new copolymer materials described by U.S. Pat. No. 5,162,445 with potential adverse effects upon its chemical inertness. Further, a significant degree of metalation at aromatic ring carbon atoms is also reported to occur with the alkyl lithium/potassium tert-pentoxide superbase reagent.
It was desirable to devise a way by which to convert the new copolymer materials into functionalized derivatives without altering the inert hydrocarbon structure of the backbone of the copolymer. In earlier applications filed by Frechet et al. U.S. Ser. Nos. 08/659,457, Jun. 6, 1996; 08/476,753, Jun. 7, 1995; 08/447,131, May 22, 1995; and 08/444,951, May 19,1995; the IB-PAS copolymer of U.S. Pat. No. 5,162,445 was effectively metalated and functionalized by adding an electrophile to a solution of the metalated IB-PAS intermediate. Such derivatization of the IB-PAS copolymer worked well for many electrophiles, including chlorotrimethyl-silane, but formed gels or cross-linked materials with certain electrophiles such as allyl bromide.
In the case of the product obtained by reacting allyl bromide with the metalated IB-PAS copolymer, the gel formation is believed to result from a metal-halogen exchange reaction and/or anionic polymerization of the allyl group. Allyl bromide could react with the metalated copolymer to form a brominated copolymer and a metal allyl. The allyl group could anionically polymerize, initiated by the benzylic bromide, or by the superbase reaction conditions.
It is also known that vinyl silane and allyl silane derivatives are subject to anionic polymerizations. See Gam et al., Polym. Prepr. (Am. Chem. Soc., Div. Polym. Chem.), 34(1), 548-9 (1993); Obu et al., Polym. J., 24(12), 1409-17 (1992). Vinyl and allyl silane derivatives would similarly have been expected to form gel under the metalation reaction conditions of U.S. Ser. No. 08/659,457.
It would be desirable to devise a way of introducing vinyl or allyl functionality on the primary benzylic carbon atoms of alkylstyrene polymers, especially on the para-methyl groups of the phenyl groups of the IB-PAS copolymers, without forming gel and without altering the inert hydrocarbon structure of the copolymer backbone.